Drying apparatus



Nov. 8, 1938.

W. A. DARRAH DRYING APPARATUS Original Filed Oct. 15, 1933 2Sheets-Sheet l ILI mW www W. A. DARRAH DRYING APPARATUS Nov. 8, 1938.

Original Filed Oct. 15, 1933 2 Sheets-Sheet 2 hun. WF.. SW 0H in -Hm 1-Patented Nov. 8, 1938 UNITED STATES PATENT OFFICE DRYING APPARATUSOriginal application October 15, 1930, Serial No. 488,852. Divided andthis application April 25,

1935, Serial No. 18,133

' 12 Claims.

This application is a division of my application Serial No. 488,852.iiled October 15, i930, now matured into Patent No. 2,000,663, issued onMay 7, 1935, which said application was in part a division ofapplication Serial No. 361,920. illed May 10, 1929, for Process ofdrying materials and apparatus therefor.

The present| invention relates to equipment and appurtenances for thedrying of materials and is particularly applicable to such objects asboards, sheets, plates and similar flattened shapes in which the ratioof surface to volume is very great. Some of the objects of thisinvention are to provide economical. simple and eilicient means fordrying such articles as wallboard, insulation board, veneer, paper,cloth and similar materials without damage. Another object oi thisinvention is to carry on drying, economically, rapidly and withoutdiscoloration oi' the material being dried.

This invention provides simple, continuous and automatic means foraccomplishing the above results. Other objects o! this invention will beapparent from a perusal oi the drawings, specilication and claimsattached hereto.

Referring to the drawings:

Figure 1 shows a side elevation partly in section of one form of mydevice;

Figure 2 shows a vertical section of one form of my device; and

Figure 3 shows a pian view partly in section of one form of my device.

Referring to the drawings, I indicates a housing or container throughwhich the material to be dried is conveyed. 2. 3 and 4 indicate severalof a series of conveying rolls for moving ma terial through my device.In place of the rolls shown, I may use any desired form of conveyormechanism such as a series oi' chains. or other commonly knownmechanism. The rolls 2, 3 and 4 indicated may each be driven by asprocket as indicated at 5, over which a continuous length o! chain 6 ispassed, serving to keep the above rolls in continuous movement atuniform rate and in the same direction. These constructional detailsform no fundamental part of my invention and are merely illustrated tomake clear one form of mechanism which I have found convenient to use.

Housing i is preferably insulated with heat retarding material 1, formedin a shell or cover around housing I. Reference numeral 8 indicates aboard about to enter my device and 9 represents aboard leaving mydevice, the direction of travel being indicated by the arrow on theboard. A heating means is shown diagrammatically at I0 connected to afan or gas moving device II. The heater may consist oi an enclosed shellof steel or other material properly insulated and arranged to burn adesired i'uel such 6 as gas, oil, coke, coal, etc. I prefer to use gasor oil, although in many cases powdered coal or other iuels may beemployed to advantage by reason of the lower cost. The exact details ofconstructionmi my heater are not of particular importance in this case,although I prefer an arrangement in which the fuel is supplied by meansof a burner I2. Burner I2 mixes the fuel with air and delivers it to acombustion chamber I3. The products oi combustion leave chamber I3 bymeans of an outlet Il and enter mixing chamber I5 between fan andcombustion chamber. The ian, which may be oi' any commercial type, isdriven by a motor or equivalent indicated by I6 and serves to maintain asubstantially continuous circulation of drying gases and products ofcombustion through the system. The gases leaving fan II pass throughdischarge duct Il and enter drier housing I, where they are distributedby al series of nozzle ducts I8; I9, 20 and 2l arranged substantiallysymmetrically. These distributing ducts serve to direct the flow of hotgases toward each end of the device, as shown by the arrows. The hotgases travel over the material being dried, preferably both above andbelow it, although if desired, on one side only. The circulating gasesreturn through openings 22 and 23 to return ducts 2l and 25 which leadto duct 2B, where they are mixed with additional products of combustionand pass through the equipment again. Ii desired, vent stack 2l and 2Bmay be placed on the equipment preferably near the ends and providedwith dampers i'or exhausting a portion of the moist gases.

In certain cases where the permissible temperatures are low, I mayexhaust the gases entirely at the ends of the equipment instead ofreturning them to be reheated. In other cases, I may pass thecirculating and drying gases in one direction only, these being detailssubject to practical operating conditions. 1

A tank or container 34 for liquid is arranged above the entrance portionof the drier and connected with a discharge duct 35 controlled by avalve 38 in such a manner as continuously to deliver liquid to therotating distributor 31 which rubs or brushes the surface of the article8 being dried. A similar brush or roll 38 supplied with 55 liquid from areservoir 39 serves to apply liquid to the underside of the board.

This equipment is particularly applicable to those installations inwhich the drying process is carried to substantial completion within thedrier and in which the operating temperatures exceed 212 F. In thesecases the discoloring eifect of sulphur and other acids is particularlymarked. This equipment is also of great importance in those cases inwhich the products of combustion are recirculated either all or in part,being reheated and delivered back to the drier.

Instead of applying the neutralizing liquid from tank 34 onto the sheetsor boards being treated, I may neutralize the effect a! the acid byadding directly to the circulating gases a proper material for absorbingor combining with the acid gases. This result may be accomplished byspraying into the discharge of circulating fan ii or introducing intothe intake l5 of said fan a finely powdered material such as soda ash,lime, etc. I prefer to use slaked lime, although quicklime willaccomplish a similar result but apparently slightly less effectively. Ihave found that ammonia is particularly eiective, and I may also spray asolution of caustic soda, soda ash, ammonia, etc.

The material should be so added as to become distributed fairlyuniformly through the circulating gases prior to the time that they comeinto Contact. with the Amaterial being treated.

According to tests which I have made, the addition of the neutralizingmaterial to the gases does not result in wholly neutralizing the sulphurin the gases. It appears, however, that the materials added collect inpart upon the sheets which are passing through the drier and in thismanner serve to neutralize the acid fumes in the circulating gases atthe time that the fumes approach the sheets. I have made tests of thegases taken from the system when the neutralizing eiect on the sheetswas quite complete and have found that the gases still give ampleevidence of a large acid content. In the case of adding a solid materialin quantity, such as hydrated lime, soda ash, etc., a certain amountwill collect and leave the drier with each sheet. This is somewhattroublesome in some cases, and in order to overcome this dlfilculty Ihave provided a series of Scrapers or brushes 39 to remove the excess ofmaterial. I may also add to one of the rolls on the discharge end of thedrier, as for example 40, a cushion or scrubber made, for example, fromastrong fabric. This will serve to remove the excess of neutralizingmaterial from the under side of the sheet.

4| indicates a tank or container for holding the alkaline material, asfor example liquefied ammonia. 42 represents a similar tank. Tanks 4Iand 42 are connected by ducts 43 and 44 respectively to the air ductsentering the drier I. As an alternative arrangement, duct 26 is shownleading from tank 42 vto the intake of fan H.

Ducts 43 and 44 are provided with control valves 45 and 46,respectively.These valves make it possible to control the relative amounts ofneutralizing material delivered into the ducts. Oil burner I2 isprovided with a control valve 48 which may be automatically or manuallyoperated as required. 'Valve 48 is mechanically interlocked with valves45 and 46, so that the opening or closing of valve 4B, thus deliveringmore or less fuel to heater i0, will automatically deliver more or lessneutralizing agent to the drier I. This mechanical interlocking isindicated diagrammatically by the cables 50 and 5i, although obviouslyany similar mechanical expedient may be employed. The lines indicatingthe dotted cable 52 and 53 show a familiar method of control in thealternative case in which the neutralizing material is added into theintake i5 of fan Il. Obviously, in most cases, eitherone or the otheralternative would be employed, as it is unnecessary to use the two.

In Figure 2 I have shown an alternative arrangement in that hopper 54delivers a supply of powdered material to the circulating gases. Hopper54 may be controlled automatically as to volume if desired. Hopper 54indicates a simple method of adding finely divided solids to thecirculating gases, accomplishing substantially the same result as in thecase of adding atomized liquids or gaseous ammonia.

In most cases I prefer to use gaseous ammonia, asI have found that verymuch smaller amounts are required to accomplish proper neutralization.Furthermore, the products which result from the neutralization whenammonia is used consist essentially of ammonium sulphate and sulphite.These substances appear under ordinary conditions as very fine powderswhose quantity is so small as to be substantially unimportant. In manyinstances, therefore, when gaseous arnmonia is used to neutralize theacid conditions, it is unnecessary to remove the resultant solid, and inmost cases a small air blast directed onto the sheet will readily removeall traces of this substance. By way of example, I have found that whendrying gypsum Wallboard with this system, and burning in theneighborhood of from forty to sixty gallons of fuel oil per hour, it isadvisable to use between fifteen and twenty pounds oi slaked lime perhour in case the oil contains around 1/2 of 1% of sulphur.

The same result may be obtained by using between one-half pound and onepound of liquid ammonia (gasied). While the liquid ammonia costsinherently much more than lime, the ease of handling it and applying it,the smaller amount of residue and the elimination of the necessity forcleaning, usually make the ammonia a more economical material.

Owing to the inherent expense per pound for ammonia, it ls advisable toapply only the amount required to neutralize the acid conditionsresulting from the fuel. In some cases, the use of a large excess ofammonia causes a difticulty, in interfering with the sizing of the sheetor board, influencing color, etc. It is therefore highly desirable, forreasons of economy and also in order to obtain the desired quality ofproduct, to proportion roughly the amount of neutralizing material addedto the amount of sulphur delivered. Under any given set of conditions,this would mean that the amount of neutralizing ma.- terial should bevaried roughly with the amount of fuel delivered to the heater, sincewith a constant grade of oil the amount of sulphur will vary with theamount of fuel burned.

I therefore have found it to great advantage to provide automatic meansas shown for varying the amount of neutralizing material with the amountof oil.

It is to be understood that the ratio should be held substantiallyconstant under any set of conditions but that a diil'erent ratio isrequired for diiferent sets of conditions. For example, if the ratioproves to be correct when one pound of ammonia iaadded to thecirculating gases for each sixty gallons of oil burned,

' combustion are mixed with assuming the oil to contain one-half of 1%oi sulphur, then if the oil should contain 1% of sulphur the amount ofammonia required would le at least twice as great, or two pounds pereach sixty gallons burned. In either case, the ratio should be heldconstant when burning varying amounts of oil having the same sulphurcontent.

I have further found that the amount of neutralizing material requiredis greater when operating at higher temperatures then when operating atlower temperatures, independent of the amount of sulphur contained inthe oil or the amount of oil burned. As a theory, I account for thisdifference as being due to the much more rapid action of the sulphuracids at the higher temperatures.

Referring now to the operation of the equipment and process which I haveinvented, it should be understood that to dry satisfactorily boards andsimilar materials they should be subjected to a stream of warm gases.mum temperature to which the boards may be subjected varies of coursewith the nature of the material from which they are formed and variousother factors. In the case of gypsum board, temperatures ranging from300 to 400 F are not unusual, while in the case of fiber board,temperatures as high as F. are frequently permissible. It will be notedthat at these temperatures the gases which convey the heat and removethe moisture are well above the dew point regardless of the amount ofmoisture carriedlby them.

I have found that drying may be accomplished satisfactorily whenoperating at the temperatures mentioned above with little regard to theamount of water carried by the circulating gases. In other words, anatmosphere consisting almost entirely of water vapor would form a veryeffective drying medium under these conditions. By returning the ilow ofcirculating gases and reheating them, I am able to reduce materially thefuel requirements for a given installation. Further, by adding theproducts of combustion directly to the circulating gases, I avoid thesc-called stack loss due to exhausting these products of combustion,which has hitherto been common practice. In general, therefore, I preferto obtain my drying continuous stream composed principally of air andwater vapor but containing also a few per cent of carbon dioxide.

It will be obvious that since the products of the circulating gases andcaused to pass continually in contact with the surface of the materialbeing dried, any substance within the products of combustion which mayhave a tendency to attack or combine with the material being dried islikely to cause damage.

It is, of course, well known that ordinary fuel oil contains appreciableamounts of sulphur and in some cases sulphuric acid as well as othermaterials such as chlorides, etc. Under the conditioris existing in thetype of equipment here disclosed, any sulphur present will be oxidizedto sulphur dioxide, which in contact with the moisture in the air and inthe board will tend to form both sulphurous and sulphuric acid. Anysulphates present in the oil due to the neutralibation of the acids usedin refining, or due to the natural impurities, will tend to form sulphurtrioxide when the oil is burned, which of course,

500 to 600"y in contact with the moisture present, will normally formsulphuric acid.

I am emphasizing the effect of sulphur and using it to describe myinvention because it is a common and marked condition and serves clearlyto illustrate my invention. I do not, however, wish to be confined tomeans for neutralizing the effect of sulphur only, as under ,someconditions other materials may be equally troublesome.

I have found that when traces of sulphuric acid are present in thecirculating gases, a portion of the acid is absorbed by the moisture onthe surface of the material being dried, with the result that thesurface of the material becomes decidedly acid.

As the drying progresses further, I have found that the water at thesurface of the board is yevaporated while the sulphuric acid produced isevaporated to a very much lesser extent. This, of course, results in theformation of a fairly concentrated acid on the surface of the materialbeing dried. If the material being dried contains large quantities oforganic material such as cellulose, starch, dextrine or othercarbohydrates, the addtionof heat will rapidly cause discoloration,which is usually objectionable, particularly in the case of dryingwallboard, insulating board, gypsum board, etc.

I have found that a concentration of acid as little as three parts inone hundred will cause a dry sheet of paper, similar to that used in thecase of gypsum wallboard, to become jet black when the temperature israised to around 400 F. The same paper without the acid will withstand atemperature of 400 F. for a limited time `without serious change ofcolor.

`When it is considered that most wallboards are used as buildingmaterials for finishing the interior of buildings an therefore, aresubjected to rigid purchasing specifications as to color, uniformity,etc., it will be appreciated that the effect of acid discoloration maybe so serious as to render the product unsalable.

In order to overcome this difficulty, I have `developed the equipmentand process' here disfound that by adding to the surface of the board orsheet before it enters the drier a solution designed `to neutralize theeffect of the acid without discoloring the surface of the board orsheet, it is possible to dry rapidly at high temperatures with directproducts of combustion under conditions which would otherwise beimpossible.

A wide range of materials may be employed, depending upon the conditionswhich must be met.

In the case of phuric acid on gypsum wallboard, I have found that bywashing the surface in the manner disclosed inthe drawings with asolution of calcium hydrate, calcium carbonate, caustic soda, sodiumsilicate, sodium carbonate, borax, soap solution, etc., the desiredresult may be obtained. It should be understood that it is not necessaryto add all of the materials specified above, as any one will beeffective if added in the proper portions. the other hand, in some casesI have found that the addition of s'everal materials mixed together insolution will give desirable results, as for example by the preventionof the formation of crystals in the surface of the board, etc. f

It will be evident from the above that the essential feature is to add amaterial which will combine with and neutralize the acid condition, thusclosed.

neutralizing the effect of sulmaintaining a concentration of acid so lowthat it will not discolor the organic materials present at the maximumtemperatures that the board or sheet is subjected to during the dryingprocess.

It is, of course, desirable to apply the material to both top and bottomsurfaces of the board, and

any time prior to drying. 'I'hus the material may be added in themanufacture of the board or sheet or, in the case of the gypsumwallboard, in the manufacture of the paper covering which is on theboard.

I have found in commercial practice that it is entirely impossible toproduce a commercially clean or salable board with certain grades o!fuel, unless the surface of the board is previously treated in themanner here outlined:

Certain materials are more satisfactory than others as neutralizers. Inthe case of a gypsum wallboard a solution of lime in water is quitesatisfactory, as the net result of the reaction is to produce calciumsulphate which is chemically similar to gypsum and which as produced inthis process is a fine White powder not directly noticeable on thesurface of the board.

Solutions of caustic soda when passed through a drier under theconditions here. speciied irequently form sodium carbonates which are inturn converted into sulphates by the action of the acid. Under someconditions. large amounts of sodium sulphate will form visible needlesor crystals which are objectionable.

'I'he addition of small amounts of sodium silicate or other gelatinousor colloidal materials will frequently prevent the formation ofnoticeable crystals on the surface of the board or sheet, and I consideras one of the decided advantages of my invention the use of a mixture ofcolloidal materials with the neutralizing compound, so that theresultant product does not form -large or unsightly or otherwiseobjectionable crystals. Traces of soap solution will serve the samepurpose under certain conditions, as will also the addition of smallamounts of commercial borax.

It should be understood that there are many possible modiiications of myinvention without departing from the spirit of this disclosure.

While I have referred primarily to fuel oil as a source of heat and alsothe source of discoloration, it should be understood that other fuelssuch as gas, coal or coke will frequently give similar My invention,Atherefore, should not be confined to devices burning oil only.

While I prefer to practice my invention by returning the gases forfurther recirculation, as this method gives greater economy, it shouldbe understood that in general the same conditions exist and the sameresults are obtained in case a stream of hot gases containing productsof combustion is circulated through the drier and then dischargedwithout employing the recirculating principle.

Obviously, many forms of driers may be employed, such as chainconveyors. oscillating mechanism, cars, etc., or the process may beemployed in the so-called batch be particularly understood that I lthese materials, and those skilled in the art will readily selectadditional materials which will be effective. In general, any compoundwhich actively combines with the acid formed will be eflecculties heredescribed.

In order to give a specific statement of conditions encountered, I wishto state that I have found that fuel oil containing 4% acid formed bedetermined in each individual case.

Having now fully described my invention. what I claim as new and wish tosecure by Letters Patent is as follow 1. An apparatus for dryingmaterials which consists of a housing, means for passing materialneutralization is uniform.

3. An apparatus for drying materials which consists of a conveyor, ahousing, a source of hot products of combustion, a device forcirculating said products of combustion through' said hous- 4. Anapparatus for drying material which consists of ahousing, means forpassing material to be dried through said housing, a combustion chamber,a device for circulating gases in contact with said material, a ductconnecting said combustion chamber with said circulating device, a ductconnecting said housing with said circulating device, and automaticallyoperable means for applying an acid-neutralizing substance directly tothe surface of said material before being dried.

5. An apparatus for drying materials which consists of a housing, asupport for said material being dried, a source tion, a deviceforcirculating said products of combustion through Said housing in contactwith said material, and means for neutralizing said products ofcombustion prior to circulation through said housing.

6. An apparatus for drying materials, consisting of a housing, a supportwithin said housing for the material being dried, a combustion chamber,a burner device delivering fuel to said oombustion chamber, a controldevice for controlling the amount of fuel delivered, a container foracidneutralizing substance, means connecting said container for saidacid-neutralizing substance with said drying apparatus, a device forcontrolling the amount of said neutralizing substance delivered, andmeans interlocking said fuel control device with the device controllingthe delivery of said acid-neutralizing substance.

7. In a drier for articles consisting of or having a surface ofcellulosic material the improvements which comprise a drier housing,means for passing combustion gases into contact with the materialtherein, means for conveying the articles through the housing, means forapplying a neutralizing material to the surface of the articles prior totheir exit from said housing, and means for removing some of saidmaterial from the surface of the articles after they are dry.

8. In a drier for articles consisting of or having a surface ofcellulosic material the improvements which comprise a drier housing,means for passing combustion gases thereinto, means for conveying thearticles through the housing, means of hot products of combus-4 forapplying a neutralizing material to the surface of the articles prior totheir admission into the drier, and means for removing some of saidmaterial from the surface of the articles after they are dry.

9. In a drier for flat boards of building material the improvementswhich comprise means for conveying the boards into, through and out ofthe drier, means for applying an acid-neutralizing material to thesurface of the boards before they encounter heated combustion gaseswhich are circulating through the drier, and means for brushingneutralized and excess neutralizing material from the boards just priorto their discharge from the drier.

l0. In a drier for articles consisting of or having a surface ofcellulosic material, the improvement which comprises a drier housing,means for passing the articles therethrough, means for producingcombustion gases, means for circulating said gases uniformly over thesurface of said material, and means for constantly injecting into saidcirculating gases a sufficient flow of neutralizing agent to maintainneutralization of the acidic substances in said housing.

11. In a drier for articles consisting of or having a surface ofcellulosic material the improvement which comprises a drier housing,means for passing the articles therethrough, a variable burner forproducing combustion gases, means for circulating said gases uniformlyover the .surface of said material, and means variable in accordancewith the variation of said burner for mixing with said gases a materialcapable of neutralizing acids contained in the gases.

12. In a drier for articles consisting of or having a surface ofcellulosic material the improvement which comprises a drier housing,means for passing the articles therethrough, a burner for producingcombustion gases, means for circulating said gases in contact with saidmaterial, means for injecting into said gases an agent capable ofneutralizing the acidic substances of said gases, and means for varyingthe injection of said neutralizing agent relative to the amount ofacidic substances in said housing.

WILLIAM A. DARRAH.

